The littoral fauna of the Danish Wadden Sea is described with respect to distribution and abundance. Samples have been collected at 19 stations in 1989. All benthic macroinvertebrates are determined, and their distributions related to sediment characteristics, water coverage time and other abiotic and biotic factors. Main emphasis has been put on the two bivalve species Cerastoderma edule and Macoma balthica. The age and size distributions of these species and their growth and production has been followed since 1989 at 2 (3) transects in the protected area around the island Langli (and Skallingen). Moreover, from 1990 plankton samples and core samples have been collected during the spawning periods, and field experiments have been carried out in order to investigate events around the settling period and the recruitment of larvae. To continue the investigations of variations in time and space of the two species in 1991, zooplankton and core samples were taken at seven transects from the beginning of the spawning period to November. With respect to the sublittoral zone, samples have been collected in 1989 and 1990 at 12 stations, representing different depths and sediment types, in the three tidal areas of the Danish Wadden Sea. The distributions and abundances of the benthic macroinvertebrates are related to various biotic and abiotic factors. Collaborative work with Arhus University, Institute of Biology, Department of Genetics and Ecology, Denmark.